Thermometer construction



May 12, 1942- F. w. wHlTLocK 2,282,441

THERMOMETER CONSTRUCTION K C O L H H W W F.

THERMOMETER CONSTRUCTION Filed April 7, 1938 2 Sheets-Sheet 2 F266/ WWwf/df h" j Patented May l2, 1942 THERMOMETER CONSTBUCTON Fred W.Whitlock, Freeport, Ill., asslgnor to Micro Switch Corporation,Freeport, Ill., a corporation of Illinois The present invention relatesgenerally to thermometers and to the taking of temperature measurementsthrough partitions, and relates also to electrical thermometers formeasuring outdoor temperatures.

In certain building temperature control devices it is desirable to takea measurement of outdoor temperature without having a, temperaturesensitive element located out of doors. This diiiiculty may be overcomeby placing the temperature sensitive element against the inside surfaceof an outside wall as, for example against the inside surface of aWindow pane. It is desirable also to measure steam temperatures by meansof thermometers located outside of the steam pipes.

Objects of the present invention include provision of an electricthermometer the temperature sensitive element of which has a highsensitivity of response to the temperature of a sur.- face against whichit lies but having a low sensitivity of response to temperatures of thespace in which it is located, the provision of -alsurface thermometerconstruction adapted to respond rapidly to changes of the surfacetemperature which it measures, the provision of an improved thermometerconstruction for measuring temperatures through partitions, and theprovision of improved electrical thermo-couple and resistancethermometer constructions. These and other objects of the invention willbecome apparent from the following description of certain specicembodiments of the invention, which embodiments serve by way of exampleto illustrate the manner in which the invention may be carried outwithout, however, limiting the invention to the details of anyparticular illustration or example. In the drawings:

Fig. 1 is a pictorial view of a temperature responsive resistance deviceconstructed in accordance with my present invention and mounted on awindow sash;

Fig. 2 is a vertical section taken along the lines 2-2 of Fig. 1 to showthe interior construction of the device;

Figs. 3, 4, and 5 illustrate a modified construction for the temperatureresponsive resistance device of Figs. 1 and 2; Fig. 3 is a detailed viewshowing the construction of the temperature response to resistanceelement; Fig. 4 is a partial longitudinal sectional view similar to theview of Fig. 2; Fig. 5 is a transverse sectional view of the modifiedtemperature responsive resistance device;

Fig. 6 is a sectional View of a thermo-couple type of temperatureresponsive device embodying my present invention Fig. 7 is a pictorialview showing the temperature responsive device of Fig. 6 mounted on awindow pane; and

Figs. 8 and 9 illustrate additional thermo-couple constructions.

In Fig. 2 a temperature responsive resistance element Ill consists of alength of copper or nickel Wire I2 wound on a fiber card I4. Thisresistance element i0 lies between two additional fiber cards I 6 and I8in the bottom of a thin walled, drawn copper box 20. The two cards Iiand I6 are of a thin compact iiber construction which provides goodelectrical insulation with a comparative good thermal conductivity.Surrounding the four margins of the ber insulating cards It. I6 and I8is a frame 22 of thermal insulating material such as felt which lls themarginal space between the edges of the liber cards and the wall of thebox 20. A layer of additional thermal insulating material covers theresistance element and the ber cards. A cover 25 nts tightly onto thebox 20 and a pair of springs 28 (of which only one appears in Fig. 2)bear against the inner surface of the cover 26 to press the resistanceelement I0 and its electrical and thermal insulating members firmly intothe bottom of the box 2li. The two terminals of the resistance elementI0 are brought out of the box in a cable through a grommetted hole atone end of the box, one end 29 of the wire I2 being carried over the bercard I 8 and embedded in the layer of thermal insulation 2d.

The temperature responsive device assembled in its box 20 and cover 26is mounted against a window pane 32, as illustrated in Figs. 1 and 2with the copper bottom of the box against the inside surface of theglass and with the cable 30 down so that moisture condensing on thewindow pane may not run into the box. A pair of brackets 34 fastened tothe sash frame support the device in position against the inside surfaceof the pane.

The outside surface of the glass is, of course, exposed to outdoor airtemperatures, but that portion of the inside surface of the glassagainst which the box lies is protected from the inuence of the indoortemperature by the box 20 itself. The copper bottom of the box 20 andthe liber cards I4 and I6 provide a comparatively small degree ofthermal insulation between the resistance wire I2 and the glass 32 andconsequently heat travels readily between the Wire I2 and the outdoorair to maintain the wire i2 at a temperature very near to that of theoutdoor air. At the same time the marginal insulating material 22 andthe insulating layer 24, togetherv with the air space overlying thelayer 24, serve to a considerable degree to thermally insulate theresistance wire l2 from the temperature of the inside air. The metal ofthe box 29 is made thin not only to improve the conductivity of heatbetween the wire I2 and the glass of the window, but also to minimizeconduction of heat from that part ci the box surface that is exposed toroom air to the portion that lies between the wire i2 and the windowglass 32. If desired the box 2li may have its marginal portionconstructed of a material of relatively low heat conductivity. It willbe apparent that the construction of the temperature responsive deviceis such that the resistance wire i2 will assume a temperature muchnearer that of the outside air than that of the inside air whichsurrounds the temperature responsive structure.

A temperature responsive device such as shown in Figs. l and 2 may beused to provide a measurement or index of the outdoor temperature forthe control of a heating system of a building. Such heating systemsgenerally are regulated to maintain substantially constant temperaturesinside the building. Accordingly, the indoor temperature will remainapproximately constant, as, ior example, at '10 degrees Fahrenheit. If,for example, the resistance wire i2 assumes an average temperature of idegrees Fahrenheit (or 30 degrees below room temperature) when theoutdoor temperature is 30 degrees Fahrenheit (40 degrees below roomtemperature), the effective thermal sensitivity of the temperatureresponsive device 'may be said to be 75% in that it experiences only 1%of the temperature change which the outside air undergoes. The specificvalue which this thermal sensitivity assumes in any given temperatureresponsive device depends in part upon the thickness and quality of thelayer of thermal insulation 2d in comparison with the thermal insulatingefect of the window pane 32 itself. Because the inside air is at adifferent temperature than that of the outside air, heat continuallypasses through the temperature responsive structure. This ilow of heatprovides a series of temperature drops through the temperatureresponsive structureand the window glass. The temperature differencebetween the inside air and. the resistance wire l2 will be high comparedto the temperature difference between the wire I2 and the outside aironly if the thermal insulation provided by the layer 24 and itsvoverlying air space is high compared to the thermal insulating eiect ofthe window glass 32 itself. The marginal thermal insulation 22 servesboth to reduce the flow of heat between the wire I2 and the sides of thecopper box 20 and also to space the wire i2 away from the sides of thebox to reduce the effect on the wire l2 of the flow oi.' heat throughthe glass itself between the covered and uncovered portions of theglass.

In the modication shown in Figs. 3. 4, and 5, the resistance wire 42instead of being wound around a ber card is looped over projections Malong'the edges of the card 46, so that all the turns of the wire lie onone face of the card. This 'card 46 is laid in the bottom of the copperbox I8 over a thin sheet of compact fiber material 59. Additional sheetsof ilber and thermal insulation are laid over the wire supporting card46, as

shown in Fig. 5 to provide a construction which 75 is otherwise similarto the construction of Figs. 1 and 2. The resistance wire 42 liesdirectly against the thin iiber insulator 60, and accordingly theconstruction of Figs. 3 and 4 places the temperature sensitiveresistance wire 4in a closer thermal relation with the outside air thandoes the construction of Fig. 2. Consequently the construction of Figs.3 and 4 responds somewhat more rapidly to changes in the outsidetemperature Y and also provides a temperature responsive device showinga slightly higher thermal sensitivity to such changes of outsidetemperature. On the other hand, the construction of Fig. 1 provides adevice which maybe constructed more easily and cheaply, and which willpermit a larger quantity of temperature responsive resistance wire to bearranged in a device of given dimensions.

In Fig. 6 a rubber suction cup 62 grips the inside surface of the windowglass 64 to support itself thereon. A bar 66 carried by the cup 62 inturn carries the temperature responsive device proper 68. Thistemperature responsive device 6B includes a pair of telescoping metalcups 10 and 12, having a spring 14 therein to' hold them normallyextended. The cup 10 is fastened to the bar 66 by means of a metalgrommet 16 and the spring 14 extends the telescoped cups to hold the endof the cup 12 against the inside surface of the window glass 6B. Thecups 16 and 12 have flanged lips 1i and 13 to prevent the spring 14 fromseparating them. The ange 1i on the outer cup is formed in a punch pressafter the other assembly operations.

A pair of thermo-couple leads and 82 are fused into a small pellet ofsolder 84- and thereby held in thermal engagement with the inside surface of the end wall of the cup 12. The two leads d0 and 132 'are ofdissimilar metals, such as, for example, iron and an alloy of copper andnickel. Suitable alloys include those marketed under the trade-marknames of Constantin and Manganin. Accordingly, the pellet of solder 84constitutes a temperature responsive junction of a thermo-couple. Sincethe end wall of the cup 12 lies directly against the window glass 64 athermo-couple junction within the pellet of solder 84 is materiallyaffected by the temperature of the air outside surface of the windowglass. The diameter of the cup 12 is made suiliciently large incomparison with the thickness of the metal from which it is formed, andin comparison with the thickness of the sheet of window glass 64, sothat the temperature of the air surrounding the cups 10 and 'l2 does nothave too great an effect upon the temperature of the thermo-couplejunction. The enclosed air space within the cups 10 and 12 provides someinsulation between the cylindrical walls of the cup 12 and the thermo,-couple wires 80 and 82. The two wires B0 and 82 are assembled into acable 86 which is threaded out through the grommet 16. The cable 86 isalso threaded through a pair of holes in the bar 66 to effectively tiethe cable to the bar. The pictorial view of Fig. 'I shows thethermo-couple device of Fig. 6 mounted upon the inside surface of awindow pane for measuring the outdoor temperature.

Fig. 8 illustrates a somewhat different thermocouple construction.Therein a rubber suction cup 92 supports itself upon the insidesurface`of a window pane 94. This suction cup 92 has a thickened portion96 through which a. pair of dissimilar metal inserts 91 and 98 extend.`Supported on the inner ends of these inserts 91 and 99 are a pair otthin resilient metal leaves 99 and |00, each leaf being of the samemetal as the insert on which it is supported. These two leaves arewelded or soldered together at a junction |02. The resilience of theleaves 99 and is such that they tend to hold the junction |02 nrmlyagainst the inside surface of the window glass 94. The inserts 91 and 98and the leaves 99 and |00 may be constructed of` any two metals havingsubstantially diierent thermoelectric potentials. Each spring leaf isconstructed of the same material as its supporting insert, so that nothermal electric potentials may be introduced into the circuit except atthe junction |02. A pair of connecting leads |04 and |06 are connectedto the outer ends of the inserts 91 and 98, each connecting lead beingof the same metal as the insert to which it is connected. These twoconnecting leads pass out through a hole in a cap |08 which fits overthe thickened portion 96 of the suction cup 92 to cover an protect theterminals.

Since each of the leaves or strips 99 and |00 is made of the same metalas its supporting insert and connecting lead, the reference junction ofthe thermo-coupleis located at the apparatus connected to the leads |06and |06. Alternatively, both of the leads |08 and |06 may be of copper,or the leads and also the inserts 9T and 98 may be of copper. In eithercase the inserts provide the reference junction. Obviously these insertswill be in much better thermal contact with the room air than with theoutdoor air. Consequently, the net potential of the thermocouplecircuit, that is the potential corresponding to the difference oftemperature between junction |02 and the inserts 91 and 98, will providea reliable index of the difference of temperature between the inside airand lthe outside air.

The construction of Fig. 8 is compact, presents an unusually neatappearance, is exceedingly simple in its construction, places thethermo-couple junction directly against the surface of the glass itself,and provides adequate air insulation in the enclosed spaced within thesuction cup 92 to reduce to a minimum the effects of extraneoustemperatures. Such extraneous eectsinclude the warming eiects of roomair upon the rubber of the suction cup 92 itself and upon the uncoveredportions of the window glass 9B. In the construction of Fig. 9 anhelical spring |2 fits snugly into a cavity on the inner face of arubber suction cup IIS. The spring ||2 at its opposite end carries athin metal cap under which is soldered a pair of dissimilar metalconductors ||6 and ||8 to provide a thermo-couple junction on the capH4. These two conductors H6 and ||8 form the two conductors i of a cablewhich is sealed through the rubber of the suction cup |`|5 itself. Thesuction cup I I6 is adapted to hold itself by suction to the insidesurface of a window pane to hold the cup H4 and its thermal junctionagainst the window glass, and to provide thermal insulation for thejunction in the same manner as the construction of Fig. 8 insulates thethermal junction |02.

The thermometers of the present invention may be employed for example inthe systems shown in my copending applications, Serial No. 189,545, ledFebruary 9, 1938, and Serial No. 200,810, filed April 7, 1938. They alsomay be used for measuring steam temperatures through the walls oi steampipes and for measuring temperatures of liquids` through the walls ofcon-l tainers.

It will be apparent to those skilled in the art that the specicconstructions, herein shown and described by way of example, may bemodified Iand varied without departing from the spirit and teachings ofthe invention. Accordingly, the invention is to be limited only inaccordance with the scope of the appended claims.

I claim:

1. In combination in a thermometer construction, a nat case having athin metal wall adapted to lie against one side of a partition in goodthermal engagement therewith, a temperature sensitive electricalresistance element, thin electrical insulation of relatively good heatconductivity between said temperature sensitive element and the thinmetal wall of said case. and a pack of heat insulating material in saidcase on the other side of said temperature sensitive element, and a packof thermal insulating material surrounding the margin of saidtemperature sensitive element within said caseso that said temperaturesensitive element engages only the central portion of said thin metalwall that is adapted to lie against the partition as aforesaid, saidpack of heat insulating material being of such size and effectiveness asto effectively insulate said temperature sensitive element from thetemperature of the space Within which said case is located, whereby saidtemperature responsive resistance element is predominantly responsive tothe temperature of the opposite side of said partition and assumes atemperature nearer to that of the opposite of said partition than tothat of said space.

2. In combination in a temperature responsive construction for athermometer for measuring temperatures through a partition, atemperature responsive element, a protective plate having a centralportion thereof in thermal engagement with said temperature responsiveelement, means for supporting said plate in good thermal engagement withone side of the partition, whereby said temperature responsive elementmust respond to the temperature to be measured through both saidpartition and said protecting plate, and means for enclosing saidtemperature responsive element for insulating it where it does notengage said plate and for insulating the margins of said platesurrounding Vsaid temperature responsive element, said insulatingenclosure being of such size that it covers margins of said platesufciently wide compared to the thickness and thermal conductivity ofsaid plate and compared to the thickness and thermal conductivity of thepartition with which said plate engages, that the path from thetemperature sensitive element through the plate and partition presents alower thermal resistance, than does the leakage path from the portion ofthe plate and partition just under the temperature responsive elementradially outward to the exposed margins of said plate and partition,whereby said temperature responsive element assumes a temperature nearerthat of the opposite side of said partition than to the temperature ofthe space on the side of the partition on which the temperatureresponsive device is located.

FRED W. WHITLOCK.

